In creases in the mass of arterial tissues and the tension on arterial walls occur with growth and with hypertension. This study is proposed in order to determine whether associated changes in the metabolism of aortic smooth muscle reflect changes in the rate of growth of the vessel or the amount of tension on the vessel wall. The rate of coversion of glucose to carbon dioxide, lactate, and lipids, and of acetate and fatty acids to carbon dioxide and tissue lipids in vitro will be compared in aortic media-intima obtained from rats of different ages and from hypertensive and normotensive rats. Younger animals have a greater rate of aortic growth than mature ones, but less stress on aortic walls; hypertensive animals have a greater rate of aortic growth and more stress on aortic walls than normotensive controls. The results of this study should show whether changes in metabolism can be related to the rate of growth of the tissue or to the amount of stress on the vessels.